An exit from the union is not the same as an isolation.
...no, but getting into quarrels with your neighbours because of territories would be!
The result of a membership in the union, is a deterioration of the national sovereignty. A common factor in the union.
Well...what's the point of being in a union if not adhering to commonly agreed laws and ways?
Both...being in and outside of a union has advantages and disadvantages...what advantages would being outside of the EU have for Poland?
Poland is no Switzerland!
So I would say, reform the union or make an exit.
What for reforms should it be?
PS: Reforming is best done from the inside ;)